A lightning current transfer assembly for a wind turbine is known, for example, from WO 2005/050008. It enables lightning current to be transferred from a rotor blade of the wind turbine to the wind turbine's nacelle by means of two electric contact arrangements. The electric contact arrangements provide galvanic connection while being movable relative to each other. They are made up of sliding contacts and a complementary belt and ring at the rotor blade and the nacelle, respectively (see e.g. FIGS. 3a and 3b of WO 2005/050008).
It has also been proposed that such a galvanic and movement-enabling electric contact arrangement can be protected from being damaged by high lightning current by means of a spark gap connected parallel to the electric contact arrangement. The electrodes forming the spark gap are movable relative to each other, as are the contact elements of the parallel electric contact arrangement. For example, one of the electrodes is a circular ring, and the other is a tip moving over the ring at a small distance. When the rotor blade is struck by lightning, the high lightning voltage will create a discharge over the spark gap, so that the lightning current does not flow through the parallel electric contact arrangement. Examples of wind turbines with such electric contact arrangements protected by parallel spark gaps are known from WO 2004/044419 A1 (sliding-contact arrangement with parallel spark gap between rotor blade and rotor hub) and EP 1 577 551 A2 (sliding-contact arrangement with parallel spark gap between rotor hub and nacelle).
Similarly, EP 1 568 883 A2 proposes that a brush contacting a contact roller of a lightning current transfer assembly for a wind turbine be protected by means of a spark gap parallel to the brush contact.
U.S. Pat. No. 6,932,574 B2 pertains to a lightning current transfer assembly for a wind turbine which also enables lightning current to be transferred from a rotor blade of the wind turbine to the wind turbine's nacelle. However, it is a different type of lightning current transfer assembly, as the gaps between the rotor blade/rotor hub and between rotor hub/nacelle are not bridged by galvanic contacts with contact members which provide galvanic connection while being movable relative to each other, but rather by spark gaps. When the rotor blade is struck by lightning, the high lightning voltage will create a discharge over the spark gap. In order to prevent charges due to static charging from accumulating in the rotor blade, a second current path is provided which provides a continuous galvanic connection path from the rotor blade to the earth, via the rotor hub. In order to prevent lightning current from taking the second current path (until the discharge across the spark gap fires), a series connection of a resistor and an inductor is interposed in the second current path.